Patent GB-887768-A (GB)
Title: Improvements in and relating to the transmission and/or recording of speech
Inventor: GABOR DENNIS
IPC: G11B20/00
Filed: 1959-03-18
Abstract: 887,768. Magnetic recording; etching. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 8, 1960 [March 18, 1959], No. 9429/59. Class 40 (2). [Also in Group XXXIX] In apparatus for compressing or expanding the bandwidth of speech signals by repeatedly scanning a progressively changing portion of a record of the signals substantially as described in Specification 645,542, records of the signal are simultaneously scanned by a plurality of sets of scanning devices. Each set operates at a different recurrence or scanning frequency and one set operating at a preferred or optimum frequency is automatically selected and used. The preferred frequency is a function of the pitch of the speech. An arrangement for simultaneously scanning magnetic tracks is described. Pick-up heads are arranged on the conical surface of a drum. Rules are given for designing the angle of the cone so as to reduce distortion. General arrangement.-Speech signals from an amplifier 1 are recorded in five parallel tracks on a magnetic tape 2. The five tracks are scanned simultaneously at different speeds by five sets of pick-up heads in a conical drum 6 whereby the original speech signal is compressed into five different bands. Each set has a different number of heads 15, Fig. 2, and has a different diameter. The output windings 16 of each set are connected in series to one of the slip rings 9 which feed the outputs to relay 4 only one of which is operated to feed the transmitter amplifier 5. The pitch discriminator 3 continuously measures the pitch of the signal and opens one relay 4 to connect to the amplifier 5 the output of the set of pick-up heads operating at the preferred frequency for that pitch. At the receiver, the signal is recorded in five tracks on magnetic tape 2<SP>1</SP> and the signal is expanded in a process which is in effect the reverse of the compressing process. The expander components 11 to 6<SP>1</SP> and 9<SP>1</SP> corresponding to compressor components 1 to 6 and 9. If the pitch is signalled in coded form from transmitter to receiver, the pitch discriminator is unnecessary. Compressor, Figs. 2, 3, 4. A conventional multiple magnetic recording head 12 has spacings between tracks at least equal to the width of one track. A rotating drum 13 comprises a number of discs 14, each disc containing a different number of heads 15 with series connector-windings 16. The leads are connected to slip rings 9 through bores 18. The tape, which is in the form of a closed, loop, is driven by a capstan 21 and a resilient roller 22 end is linked with an erasing head not shown. Fig. 6 shows the paths 24 of the scanning heads over the tape, R being the position of the recorder 12. The tracks 23 are effectively scanned when the tracks and the heads coincide for a short distance. The same device may be used as an expander if the tape and the drum are run in opposite directions. Receiver, Fig. 9.-The tape is run clockwise from the recording head 12 over a conical saddle-piece 26 to a magazine 27 before returning to the recording head via an eraser 25. The drum 13 rotates anti-clockwise and contains heads 15 on the face of a conical cavity, the face being closely spaced from the tape 2<SP>1</SP>. Specifications 616,156 and 682,322 also are referred to.